A hybrid vehicle may include an engine and an electric machine to propel the hybrid vehicle. The engine may be operated during higher torque demands and the electric machine may be operated solely at lower torque demands and in combination with the engine at higher torque demands. The electric machine may also convert the hybrid vehicle's kinetic energy into electrical energy that may be used at a later time. The electrical energy that is converted from the hybrid vehicle's kinetic energy may be important for restoring charge in the vehicle's battery so that the electric machine may continue to provide positive torque to the hybrid vehicle driveline after the hybrid vehicle has been driven for longer distances. In addition, if the hybrid vehicle is driven on a closed track for racing or other demonstration purposes, there may be fewer opportunities to charge the battery via the electric machine because vehicle deceleration may transfer normal forces from driven wheels to non-driven wheels. Therefore, it may be desirable to increase the opportunities to provide charge from an electric machine to vehicle batteries or other electric energy storage devices.
The inventors herein have recognized the above-mentioned issues and have developed a driveline operating method, comprising: charging an electric energy storage device solely via a rear drive unit electric machine in response to a regenerative torque of the rear drive unit electric machine not being substantially equal to a rear drive unit electric machine torque threshold; and charging an electric energy storage device via the rear drive unit electric machine and an integrated starter/generator in response to a regenerative torque of the rear drive unit electric machine being substantially equal to the rear drive unit electric machine torque threshold.
Electric charge may be provided to a battery or other alternative electric energy storage device solely via a rear drive unit when the amount of requested regenerative braking is low. However, when higher amounts of regenerative braking are requested, the battery may be supplied charge via a rear drive unit electric machine and an integrated starter/generator. Thus, battery charging may be performed with more than one electric machine in the driveline. Further, the rear drive unit may be assigned a higher battery charging priority level so that the life of the second electric machine may be extended.
The present description may provide several advantages. In particular, the approach may improve coordination of electric machines used for regenerative braking. Additionally, the approach may increase an amount of charge that may be supplied to a battery when a vehicle is operated on a closed race or testing road circuit. Further, the approach may change ways charge may be delivered to a battery in response to urgency of recharging the vehicle's battery.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.